<?php
if(isset($_REQUEST['your_param_name'])){
  // Do stuff here like save the parameter passed in
?>
Thank you for submitting the form.
<?php
} else {
?>
Render the page normally with the form here.
<form action="" method="post">
  <label for="your_param_name">Param Name: </label>
  <input id="your_param_name" type="input" name="your_param_name" />
  <input type="submit" value="Submit Form" />
</form>
<?php
}
?>